Car exhaust often contains environmentally and biologically harmful compositions, including hydrocarbons, carbon monoxide, and nitrogen oxide. Some of these compositions come from incomplete combustion of gasoline or other fuels. These compositions are often formed in the high temperature environment of the engines.
Catalytic converters are used to convert these environmentally and biologically harmful compositions into less or non-environmentally harmful compositions, such as carbon dioxide, water, nitrogen, and oxygen. A catalytic converter typically includes a catalytic converter core that is coated with a catalyst-containing washcoat. The core of the catalytic converter normally includes a grid array structure that provides a large surface area to support the catalysts. The washcoats generally contain silica and alumina, which provide an even larger surface area for active precious metal catalysts. The active precious metal catalysts often include platinum, palladium, and rhodium. Other metals that are also catalytically active can also be used as catalysts, such as cerium, iron, manganese, and nickel.
Two types of catalytic converters are generally available, two-way and three-way catalytic converters. The three-way catalytic converter is widely used on gasoline engines to reduce the emission of hydrocarbons, carbon monoxide, and nitrogen oxides. With the assistance of the active catalysts, the carbon monoxide and hydrocarbons are oxidized and converted into carbon dioxide, and the nitrogen oxides are reduced and converted into nitrogen, as shown below in the below Equations.2CO+O2→2CO2 CxH2x+2+[(3x+1)/2]O2→xCO2+(x+1)H2O2NO+2CO→2CO2+N2 CxH2x+2+NO→xCO2+H2O+N2 
Traditionally, the three-way catalytic converters are prepared by separately mixing oxidative precious metals, such as platinum or palladium, with aluminum oxide, water, and other components to make a slurry in one container and mixing reductive precious metal, such as rhodium, with cerium zirconium oxide, water, and other components to make a second slurry in a second container. The slurries are normally referred to as oxidative and reductive washcoats. A ceramic monolith, which can be cylindrically shaped, having a grid array structure is dipped into one of the washcoats to form a first catalytic layer on the ceramic monolith. After drying and calcining, the ceramic monolith is dipped into another washcoat to form a second layer on the ceramic monolith. The ceramic monolith including the two washcoat layers is fitted into a shell of a catalytic converter, which connects to the engine for treating exhaust gas.
Catalytic converters made by traditional methods suffer from problems. One big problem is that traditional catalysts age over time, due to the exposure to the high temperature exhaust gases. During normal operation, the temperature within a typical gasoline engine catalytic converter can 1,000 degrees ° F., or in some instances even higher. These high temperatures give the precious metal nano-particles in the washcoat layer increased mobility—which results in these particles moving more quickly through the washcoat layers. When the precious metal nano-particles encounter one another as they move through the washcoat layer, they can sinter or coalesce into larger metal particles in a phenomenon known as “aging.” This aging phenomenon results in the loss of available reactive surfaces of the precious metals. Accordingly, through aging catalytic converters become less effective, the light-off temperature starts to rise, and emissions levels start to rise.
The aging phenomenon is even more of an issue in gasoline engines that use three ways catalytic converters than in diesel engines that can use two-way catalytic converters. This is because the exhaust temperature of a gasoline exhaust is higher than the temperature of a diesel exhaust. In addition, the three-way catalytic converter has to deal with both the aging of the oxidation and the reduction catalysts. To counteract these aging effects, catalytic converter manufacturers can increase the amount of precious metal particles initially present in the catalytic converter. However, increasing the amount of precious metal in the converter is both expensive and wasteful.
Accordingly, better materials and methods to prepare the three-way active catalytic materials are needed.